package org.apache.lucene.index;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/**
 * This is a {@link LogMergePolicy} that measures size of a segment as the
 * number of documents (not taking deletions into account).
 */

public class LogDocMergePolicy extends LogMergePolicy {

	/**
	 * Default minimum segment size.
	 * 
	 * @see setMinMergeDocs
	 */
	public static final int DEFAULT_MIN_MERGE_DOCS = 1000;

	public LogDocMergePolicy() {
		super();
		minMergeSize = DEFAULT_MIN_MERGE_DOCS;

		// maxMergeSize is never used by LogDocMergePolicy; set
		// it to Long.MAX_VALUE to disable it
		maxMergeSize = Long.MAX_VALUE;
	}

	protected long size(SegmentInfo info) {
		return info.docCount;
	}

	/**
	 * Sets the minimum size for the lowest level segments. Any segments below
	 * this size are considered to be on the same level (even if they vary
	 * drastically in size) and will be merged whenever there are mergeFactor of
	 * them. This effectively truncates the "long tail" of small segments that
	 * would otherwise be created into a single level. If you set this too
	 * large, it could greatly increase the merging cost during indexing (if you
	 * flush many small segments).
	 */
	public void setMinMergeDocs(int minMergeDocs) {
		minMergeSize = minMergeDocs;
	}

	/***************************************************************************
	 * Get the minimum size for a segment to remain un-merged.
	 * 
	 * @see #setMinMergeDocs
	 **************************************************************************/
	public int getMinMergeDocs() {
		return (int) minMergeSize;
	}
}
